1. Technical Field
This disclosure relates to digital video processing methods and apparatus. More particularly, the disclosure relates to image quality improvement by removal of banding artifacts, also known as banding noise.
2. Discussion of the Related Art
Banding artifacts, or banding noise, in a digital image or video sequence can be caused by quantization of gray scale values or color values and may appear as a false contour effect in a smooth region of the image. False contours may appear as bands in a uniform or continuously varying area of the image.
Techniques have been proposed for removing banding artifacts from digital images. In one approach, a method for detecting digital contours utilizes a selected one of a plurality of search window sizes based on a corresponding variance of the image, and removes the digital contour by using a low pass filter matched to the selected search window size. Another approach utilizes a block based texture/flat area classification by analyzing the coded block maximum/minimum edge value and utilizing a debanding filter with adaptive window size based on the texture/flat classification results.
Conventional debanding techniques have various drawbacks, including but not limited to undesired side effects on image quality and high implementation cost. The effectiveness of known debanding filters increases with filter kernel size, but large filters have a high implementation cost. Accordingly, there is the need for improved methods and apparatus for filtering banding noise in digital image signals.